Wireless communication systems are widely deployed to provide various types of communications such as voice, data, video, etc. These systems may be multiple-access systems capable of supporting communication with multiple access terminals by sharing available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE) systems, and orthogonal frequency division multiple access (OFDMA) systems. Typically, a wireless communication system comprises several base stations, wherein each base station communicates with a mobile station using a forward link and each mobile station (or access terminal) communicates with base station(s) using a reverse link.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out (SISO), multiple-in-signal-out (MISO) or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min {NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
A MIMO system supports a time division duplex (TDD) and frequency division duplex (FDD) systems. In a TDD system, the forward and reverse link transmissions are on the same frequency region so that the reciprocity principle allows the estimation of the forward link channel from the reverse link channel. This enables the eNode B to extract transmit beamforming gain on the forward link when multiple antennas are available at the eNode B.
When a user generates data for transmission, a service request is conveyed to the base station or an eNode B via established communication channels and in turn the base station assigns resources contingent upon time, bandwidth requirements/availability or service options of the user. The access terminal of the user or user equipment (UE) accordingly utilizes the assigned resources for communicating with the eNode B via the uplink. However, various factors such as power constraints, signal attenuation, obstacles, etc. can lead to fluctuations in transmission from the UE. As a result, the eNode B transmits power control signals to the UE based on the transmissions received from the UE thereby facilitating the UE to transmit with optimal power. However, the resources assigned for transmitting power control commands are assigned statically so that even if a UE is not transmitting or transmitting at optimum power levels, resources for power control commands remain assigned thereby leading to a non-optimal use of resources within the wireless communication system.